NCERT CBSE Standard 12 Organic Chemistry Aldehydes, Ketones, Carboxylic Acids Chapter 12
Chapter 12 :
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Wolff Kishner reduction
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Aldehyde preparation methods
Methods of preparing Ketones
Mechanism of Beckmann Rearrangement
Keto Enol Tautomerism
Pinacol Pinacolone Rearrangement
Acid preparation methods
Halogenation of acids Hell Volhard Zelinsky reaction
General Properties of Ketones
Gyan Question when acetaldehyde is heated in Fehling’s solution
The red precipitates are due to Cu2O
Ans : Benzaldehyde does not react with Fehling’s solution
Oxydation of Carbonyl Group
Note Pink Colour
Boiling point order of acids
Some Named reactions
Reagents used in reduction
Tischenko Reaction :
Gyan Question order of base strength of leaving group
Gyan Question mechanism of nucleophile acyl substitution
Activity of acid derivative
Order of Leaving group ability
Extra Questions in Aldehydes, Ketones, Carboxylic Acid NCERT CBSE Standard 12 India.
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12.1.2 Structure of the Carbonyl Group The carbonyl carbon atom is sp -hybridised and forms three sigma (σ) bonds. The fourth valence electron of carbon remains in its p-orbital and forms a π-bond with oxygen by overlap with p-orbital of an oxygen. In addition, the oxygen atom also has two non bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane. The bond angles are approximately 120° as expected of a trigonal coplanar structure (Figure 12.1).
The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have substantial dipole moments and are polar than ethers. The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral (A) and a dipolar (B) structures as shown.
Intext Questions 12.1 Write the structures of the following compounds.
(i) α-Methoxypropionaldehyde (ii) 3-Hydroxybutanal (iii) 2-Hydroxycyclopentane carbaldehyde (iv) 4-Oxopentanal (v) Di-sec. butyl ketone (vi) 4-Fluoroacetophenone 12.2 Preparation of Aldehydes and Ketones Some important methods for the preparation of aldehydes and ketones are as follows:
12.2.1 Preparation of Aldehydes and Ketones 1. By oxidation of alcohols Aldehydes and ketones are generally prepared by oxidation of primary and secondary alcohols, respectively (Unit 11, Class XII).
2. By dehydrogenation of alcohols This method is suitable for volatile alcohols and is of industrial application. In this method alcohol vapours are passed over heavy metal catalysts (Ag or Cu). Primary and secondary alcohols give aldehydes and ketones, respectively (Unit 11, Class XII).
3. From hydrocarbons (i) By ozonolysis of alkenes: As we know, ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both depending on the substitution pattern of the alkene (Unit 13, Class XI).
(ii) By hydration of alkynes: Addition of water to ethyne in the presence of H2SO4 and HgSO4 gives acetaldehyde. All other alkynes give ketones in this reaction (Unit 13, Class XI).
12.2.2 Preparation of Aldehydes 1. From acyl chloride (acid chloride) Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction.
3. From hydrocarbons Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons by the following methods:
(i) By oxidation of methylbenzene Strong oxidising agents oxidise toluene and its derivatives to benzoic acids. However, it is possible to stop the oxidation at the aldehyde stage with suitable reagents that convert the methyl group to an intermediate that is difficult to oxidise further. The following methods are used for this purpose. (a) Use of chromyl chloride (CrO2Cl2): Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.
This reaction is called Etard reaction. (b) Use of chromic oxide (CrO3):
Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be hydrolysed to corresponding benzaldehyde with aqueous acid. (ii) By side chain chlorination followed by hydrolysis Side chain chlorination of toluene gives benzal chloride, which on hydrolysis gives benzaldehyde. This is a commercial method of manufacture of benzaldehyde.
(iii) By Gatterman – Koch reaction When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde.
12.2.3 Preparation of Ketones 1. From acyl chlorides
Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones.
2. From nitriles Treating a nitrile with Grignard reagent followed by hydrolysis yields a ketone. 3. From benzene or substituted benzenes When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminium chloride, it affords the corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction.
Give names of the reagents to bring about the following transformations: (i) Hexan-1-ol to hexanal (ii) Cyclohexanol to cyclohexanone (iii) p-Fluorotoluene to p-fluorobenzaldehyde (iv) Ethanenitrile to ethanal (v) Allyl alcohol to propenal (vi) But-2-ene to ethanal
Solution (i) C5H5NH+CrO3Cl-(PCC) (ii) K2Cr2O7 in acidic medium (iii) CrO3 in the presence of acetic anhydride/ 1. CrO2Cl22. HOH (iv) (Diisobutyl)aluminium hydride (DIBAL-H) (v) PCC (vi) O3/H2O-Zn dust Intext Question 12.2 Write the structures of products of the following reactions;
12.3 Physical properties The physical properties of aldehydes and ketones are described as follows. Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding. The following compounds of molecular masses 58 and 60 are ranked in order of increasing boiling points.
However, the solubility of aldehydes and ketones decreases rapidly on increasing the length of alkyl chain. All aldehydes and ketones are fairly soluble in organic solvents like benzene, ether, methanol, chloroform, etc. The lower aldehydes have sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent and more fragrant. In fact, many naturally occurring aldehydes and ketones are used in the blending of perfumes and flavouring agents.
Example 12.2 Arrange the following compounds in the increasing order of their boiling points: CH3CH2CH2CHO, CH3CH2CH2CH2OH, H5C2-O-C2H5, CH3CH2CH2CH2CH3
Solution The molecular masses of these compounds are in the range of 72 to 74. Since only butan-1-ol molecules are associated due to extensive intermolecular hydrogen bonding, therefore, the boiling point of butan-1-ol would be the highest. Butanal is more polar than ethoxyethane. Therefore, the intermolecular dipole-dipole attraction is stronger in the former. n-Pentane molecules have only weak van der Waals forces. Hence increasing order of boiling points of the given compounds is as follows: CH3CH2CH2CH2CH3 < H5C2-O-C2H5 < CH3CH2CH2CHO < CH3CH2CH2CH2OH
Intext Question 12.3 Arrange the following compounds in increasing order of their boiling points. CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH3
12.4 Chemical Reactions Since aldehydes and ketones both possess the carbonyl functional group, they undergo similar chemical reactions.
1. Nucleophilic addition reactions Contrary to electrophilic addition reactions observed in alkenes (refer Unit 13, Class XI), the aldehydes and ketones undergo nucleophilic addition reactions.
(i) Mechanism of nucleophilic addition reactions A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp2 hybridised orbitals of carbonyl carbon (Fig. 12.2). The hybridisation of carbon changes from sp2 to sp3 in this process, and a tetrahedral alkoxide intermediate is produced. This intermediate captures a proton from the reaction medium to give the electrically neutral product. The net result is addition of Nu− and H+ across the carbon oxygen double bond as shown in Fig. 12.2.
(ii) Reactivity Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl more effectively than in former.
Example 12.3 Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal? Explain your answer.
Solution The carbon atom of the carbonyl group of benzaldehyde is less electrophilic than carbon atom of the carbonyl group present in propanal. The polarity of the carbonyl group is reduced in benzaldehyde due to resonance as shown below and hence it is less reactive than propanal.
(iii) Some important examples of nucleophilic addition and nucleophilic addition-elimination reactions:
(a) Addition of hydrogen cyanide (HCN): Aldehydes and ketones react with hydrogen cyanide (HCN) to yield cyanohydrins. This reaction occurs very slowly with pure HCN. Therefore, it is catalysed by a base and the generated cyanide ion (CN−) being a stronger nucleophile readily adds to carbonyl compounds to yield corresponding cyanohydrin. Cyanohydrins are useful synthetic intermediates.
(b) Addition of sodium hydrogensulphite: Sodium hydrogensulphite adds to aldehydes and ketones to form the addition products. The position of the equilibrium lies largely to the right hand side for most aldehydes and to the left for most ketones due to steric reasons. The hydrogensulphite addition compound is water soluble and can be converted back to the original carbonyl compound by treating it with dilute mineral acid or alkali. Therefore, these are useful for separation and purification of aldehydes.
(c) Addition of Grignard reagents: (refer Unit 11, Class XII).
(d) Addition of alcohols: Aldehydes react with one equivalent of monohydric alcohol in the presence of dry hydrogen chloride to yield alkoxyalcohol intermediate, known as hemiacetals, which further react with one more molecule of alcohol to give a gem-dialkoxy compound known as acetal as shown in the reaction. Ketones react with ethylene glycol under similar conditions to form cyclic products known as ethylene glycol ketals.
Dry hydrogen chloride protonates the oxygen of the carbonyl compounds and therefore, increases the electrophilicity of the carbonyl carbon facilitating the nucleophilic attack of ethylene glycol. Acetals and ketals are hydrolysed with aqueous mineral acids to yield corresponding aldehydes and ketones respectively.
(e) Addition of ammonia and its derivatives: Nucleophiles, such as ammonia and its derivatives H2N-Z add to the carbonyl group of aldehydes and ketones. The reaction is reversible and catalysed by acid. The equilibrium favours the product formation due to rapid dehydration of the intermediate to form >C=N-Z. Z = Alkyl, aryl, OH, NH2, C6H5NH, NHCONH2, etc.
2. Reduction (i) Reduction to alcohols: Aldehydes and ketones are reduced to primary and secondary alcohols respectively by sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4) as well as by catalytic hydrogenation (Unit 11, Class XII). (ii) Reduction to hydrocarbons: The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with zinc- amalgam and concentrated hydrochloric acid [Clemmensen reduction] or with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol (Wolff-Kishner reduction).
3. Oxidation Aldehydes differ from ketones in their oxidation reactions. Aldehydes are easily oxidised to carboxylic acids on treatment with common oxidising agents like nitric acid, potassium permanganate, potassium dichromate, etc. Even mild oxidising agents, mainly Tollens’ reagent and Fehlings’ reagent also oxidise aldehydes.
Ketones are generally oxidised under vigorous conditions, i.e., strong oxidising agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.
The mild oxidising agents given below are used to distinguish aldehydes from ketones:
(i) Tollens’ test: On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’ reagent), a bright silver mirror is produced due to the formation of silver metal. The aldehydes are oxidised to corresponding carboxylate anion. The reaction occurs in alkaline medium.
(ii) Fehling’s test: Fehling reagent comprises of two solutions, Fehling solution A and Fehling solution B. Fehling solution A is aqueous copper sulphate and Fehling solution B is alkaline sodium potassium tartarate (Rochelle salt). These two solutions are mixed in equal amounts before test. On heating an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained. Aldehydes are oxidised to corresponding carboxylate anion. Aromatic aldehydes do not respond to this test.
(iii) Oxidation of methyl ketones by haloform reaction: Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform. This oxidation does not affect a carbon-carbon double bond, if present in the molecule. Iodoform reaction with sodium hypoiodite is also used for detection of CH3CO group or CH3CH(OH) group which produces CH3CO group on oxidation.
Example 12.4 An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2,4-DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens’ or Fehlings’ reagent, nor does it decolourise bromine water or Baeyer’s reagent. On drastic oxidation with chromic acid, it gives a carboxylic acid (B) having molecular formula C7H6O2. Identify the compounds (A) and (B) and explain the reactions involved.
Solution (A) forms 2,4-DNP derivative. Therefore, it is an aldehyde or a ketone. Since it does not reduce Tollens’ or Fehling reagent, (A) must be a ketone. (A) responds to iodoform test. Therefore, it should be a methyl ketone. The molecular formula of (A) indicates high degree of unsaturation, yet it does not decolourise bromine water or Baeyer’s reagent. This indicates the presence of unsaturation due to an aromatic ring. Compound (B), being an oxidation product of a ketone should be a carboxylic acid. The molecular formula of (B) indicates that it should be benzoic acid and compound (A) should, therefore, be a monosubstituted aromatic methyl ketone. The molecular formula of (A) indicates that it should be phenyl methyl ketone (acetophenone). Reactions are as follows:
4. Reactions due to a-hydrogen Acidity of α-hydrogens of aldehydes and ketones: The aldehydes and ketones undergo a number of reactions due to the acidic nature of α-hydrogen. The acidity of α-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base.
(i) Aldol condensation: Aldehydes and ketones having at least one α-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol), respectively. This is known as Aldol reaction.
The name aldol is derived from the names of the two functional groups, aldehyde and alcohol, present in the products. The aldol and ketol readily lose water to give α,β-unsaturated carbonyl compounds which are aldol condensation products and the reaction is called Aldol condensation. Though ketones give ketols (compounds containing a keto and alcohol groups), the general name aldol condensation still applies to the reactions of ketones due to their similarity with aldehydes.
(ii) Cross aldol condensation: When aldol condensation is carried out between two different aldehydes and / or ketones, it is called cross aldol condensation. If both of them contain α-hydrogen atoms, it gives a mixture of four products. This is illustrated below by aldol reaction of a mixture of ethanal and propanal.
5. Other reactions
(i) Cannizzaro reaction: Aldehydes which do not have an α-hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.
Intext Questions 12.4 Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions. (i) Ethanal, Propanal, Propanone, Butanone. (ii) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone. Hint: Consider steric effect and electronic effect. 12.5 Predict the products of the following reactions:
12.5 Uses of Aldehydes and Ketones
In chemical industry aldehydes and ketones are used as solvents, starting materials and reagents for the synthesis of other products. Formaldehyde is well known as formalin (40%) solution used to preserve biological specimens and to prepare bakelite (a phenol-formaldehyde resin), urea-formaldehyde glues and other polymeric products. Acetaldehyde is used primarily as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs. Benzaldehyde is used in perfumery and in dye industries. Acetone and ethyl methyl ketone are common industrial solvents. Many aldehydes and ketones, e.g., butyraldehyde, vanillin, acetophenone, camphor, etc. are well known for their odours and flavours. Carboxylic Acids Carbon compounds containing a carboxyl functional group, –COOH are called carboxylic acids. The carboxyl group, consists of a carbonyl group attached to a hydroxyl group, hence its name carboxyl. Carboxylic acids may be aliphatic (RCOOH) or aromatic (ArCOOH) depending on the group, alkyl or aryl, attached to carboxylic carbon. Large number of carboxylic acids are found in nature. Some higher members of aliphatic carboxylic acids (C12 – C18) known as fatty acids, occur in natural fats as esters of glycerol. Carboxylic acids serve as starting material for several other important organic compounds such as anhydrides, esters, acid chlorides, amides, etc.
12.6 Nomenclature and Struture of Carbonyl Group 12.6.1 Nomenclature Since carboxylic acids are amongst the earliest organic compounds to be isolated from nature, a large number of them are known by their common names. The common names end with the suffix –ic acid and have been derived from Latin or Greek names of their natural sources. For example, formic acid (HCOOH) was first obtained from red ants (Latin: formica means ant), acetic acid (CH3COOH) from vinegar (Latin: acetum, means vinegar), butyric acid (CH3CH2CH2COOH) from rancid butter (Latin: butyrum, means butter). In the IUPAC system, aliphatic carboxylic acids are named by replacing the ending –e in the name of the corresponding alkane with – oic acid. In numbering the carbon chain, the carboxylic carbon is numbered one. For naming compounds containing more than one carboxyl group, the ending –e of the alkane is retained. The number of carboxyl groups are indicated by adding the multiplicative prefix, di, tri, etc. to the term oic. The position of –COOH groups are indicated by the arabic numeral before the multiplicative prefix. Some of the carboxylic acids along with their common and IUPAC names are listed in Table 12.3.
12.6.2 Structure of Carboxyl Group In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120°. The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure shown below:
12.7 Methods of Preparation of Carboxylic Acids
Some important methods of preparation of carboxylic acids are as follows.
1. From primary alcohols and aldehydes Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate (KMnO4) in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7) and chromium trioxide (CrO3) in acidic media.
Carboxylic acids are also prepared from aldehydes by the use of mild oxidising agents (Section 12.4).
2. From alkylbenzenes Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to the carboxyl group irrespective of length of the side chain. Primary and secondary alkyl groups are oxidised in this manner while tertiary group is not affected. Suitably substituted alkenes are also oxidised to carboxylic acids with these oxidising reagents (refer Unit 13, Class XI).
4. From Grignard reagents Grignard reagents react with carbon dioxide (dry ice) to form salts of carboxylic acids which in turn give corresponding carboxylic acids after acidification with mineral acid.
As we know, the Grignard reagents and nitriles can be prepared from alkyl halides (refer Unit 10, Class XII). The above methods (3 and 4) are useful for converting alkyl halides into corresponding carboxylic acids having one carbon atom more than that present in alkyl halides (ascending the series).
5. From acyl halides and anhydrides Acid chlorides when hydrolysed with water give carboxylic acids or more readily hydrolysed with aqueous base to give carboxylate ions which on acidification provide corresponding carboxylic acids. Anhydrides on the other hand are hydrolysed to corresponding acid(s) with water.
Example 12.5 Write chemical reactions to affect the following transformations: (i) Butan-1-ol to butanoic acid (ii) Benzyl alcohol to phenylethanoic acid (iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid (iv) 4-Methylacetophenone to benzene-1,4-dicarboxylic acid (v) Cyclohexene to hexane-1,6-dioic acid (vi) Butanal to butanoic acid.
Intext Question 12.7
Show how each of the following compounds can be converted to benzoic acid.
(i) Ethylbenzene (ii) Acetophenone (iii) Bromobenzene (iv) Phenylethene (Styrene)
12.8 Physical Properties Aliphatic carboxylic acids upto nine carbon atoms are colourless liquids at room temperature with unpleasant odours. The higher acids are wax like solids and are practically odourless due to their low volatility. Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding. The hydrogen bonds are not broken completely even in the vapour phase. In fact, most carboxylic acids exist as dimer in the vapour phase aprotic solvent or in the aprotic solvents. Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water due to the formation of hydrogen bonds with water. The solubility decreases with increasing number of carbon atoms. Higher carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon part. Benzoic acid, the simplest aromatic carboxylic acid is nearly insoluble in cold water. Carboxylic acids are Hydrogen bonding of also soluble in less polar organic solvents like benzene, RCOOH with H2O ether, alcohol, chloroform, etc.
12.9 Chemical Reactions The reaction of carboxylic acids are classified as follows:
12.9.1 Reactions Involving Cleavage of O–H Bond Acidity Reactions with metals and alkalies The carboxylic acids like alcohols evolve hydrogen with electropositive metals and form salts with alkalies similar to phenols. However, unlike phenols they react with weaker bases such as carbonates and hydrogencarbonates to evolve carbon dioxide. This reaction is used to detect the presence of carboxyl group in an organic compound.
Carboxylic acids dissociate in water to give resonance stabilised carboxylate anions and hydronium ion.
For the above reaction:
for the above reaction:
where Keq, is equilibrium constant and Ka is the acid dissociation constant. For convenience, the strength of an acid is generally indicated by its pKa value rather than its Ka value. pKa = – log Ka The pKa of hydrochloric acid is –7.0, where as pKa of trifluoroacetic acid (the strongest organic acid), benzoic acid and acetic acid are 0.23,4.19 and 4.76, respectively. Smaller the pKa, the stronger the acid ( the better it is as a proton donor). Strong acids have pKa values < 1, the acids with pKa values between 1 and 5 are considered to be moderately strong acids, weak acids have pKa values between 5 and 15, and extremely weak acids have pKa values >15. Carboxylic acids are weaker than mineral acids, but they are stronger acids than alcohols and many simple phenols (pKa is ~16 for ethanol and 10 for phenol). In fact, carboxylic acids are amongst the most acidic organic compounds you have studied so far. You already know why phenols are more acidic than alcohols. The higher acidity of carboxylic acids as compared to phenols can be understood similarly. The conjugate base of carboxylic acid, a carboxylate ion, is stabilised by two equivalent resonance structures in which the negative charge is at the more electronegative oxygen atom. The conjugate base of phenol, a phenoxide ion, has non-equivalent resonance structures in which the negative charge is at the less electronegative carbon atom. Therefore, resonance in phenoxide ion is not as important as it is in carboxylate ion. Further, the negative charge is delocalised over two electronegative oxygen atoms in carboxylate ion whereas it is less effectively delocalised over one oxygen atom and less electronegative carbon atoms in phenoxide ion (Unit 11, Class XII). Thus, the carboxylate ion is more stabilised than phenoxide ion, so carboxylic acids are more acidic than phenols. Effect of substituents on the acidity of carboxylic acids: Substituents may affect the stability of the conjugate base and thus, also affect the acidity of the carboxylic acids. Electron withdrawing groups increase the acidity of carboxylic acids by stabilising the conjugate base through delocalisation of the negative charge by inductive and/or resonance effects. Conversely, electron donating groups decrease the acidity by destabilising the conjugate base.
Direct attachment of groups such as phenyl or vinyl to the carboxylic acid, increases the acidity of corresponding carboxylic acid, contrary to the decrease expected due to resonance effect shown below: This is because of greater electronegativity of sp hybridised carbon to which carboxyl carbon is attached. The presence of electron withdrawing group on the phenyl of aromatic carboxylic acid increases their acidity while electron donating groups decrease their acidity.
12.9.2 Reactions Involving Cleavage of C–OH Bond 1.
Formation of anhydride Carboxylic acids on heating with mineral acids such as H2SO4 or with P2O5 give corresponding anhydride.
Mechanism of esterification of carboxylic acids: The esterification of carboxylic acids with alcohols is a kind of nucleophilic acyl substitution. Protonation of the carbonyl oxygen activates the carbonyl group towards nucleophilic addition of the alcohol. Proton transfer in the tetrahedral intermediate converts the hydroxyl group into – +OH2 group, which, being a better leaving group, is eliminated as neutral water molecule. The protonated ester so formed finally loses a proton to give the ester.
3. Reactions with PCl5, PCl3 and SOCl2 The hydroxyl group of carboxylic acids, behaves like that of alcohols and is easily replaced by chlorine atom on treating with PCl5, PCl3 or SOCl2. Thionyl chloride (SOCl2) is preferred because the other two products are gaseous and escape the reaction mixture making the purification of the products easier. RCOOH + PCl5 → RCOCl + POCl3 +HCl 3RCOOH + PCl3 → 3RCOCl + H3PO3 RCOOH + SOCl2 → RCOCl + SO2 +HCl
4. Reaction with ammonia Carboxylic acids react with ammonia to give ammonium salt which on further heating at high temperature give amides. For example:
12.9.3 Reactions Involving –COOH Group 1. Reduction Carboxylic acids are reduced to primary alcohols by lithium aluminium hydride or better with diborane. Diborane does not easily reduce functional groups such as ester, nitro, halo, etc. Sodium borohydride does not reduce the carboxyl group.
2. Decarboxylation Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaO in the ratio of 3 : 1).
The reaction is known as decarboxylation.
Alkali metal salts of carboxylic acids also undergo decarboxylation on electrolysis of their aqueous solutions and form hydrocarbons having twice the number of carbon atoms present in the alkyl group of the acid. The reaction is known as Kolbe electrolysis (Unit 13, Class XI).
12.9.4 Substitution Reactions in the Hydrocarbon
Part 1. Halogenation Carboxylic acids having an α-hydrogen are halogenated at the α-position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give α-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.
2. Ring substitution Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a deactivating and meta-directing group. They however, do not undergo Friedel-Crafts reaction (because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group).
12.10 Uses of Carbxoylic Acids Methanoic acid is used in rubber, textile, dyeing, leather and electroplating industries. Ethanoic acid is used as solvent and as vinegar in food industry. Hexanedioic acid is used in the manufacture of nylon-6, 6. Esters of benzoic acid are used in perfumery. Sodium benzoate is used as a food preservative. Higher fatty acids are used for the manufacture of soaps and detergents.
Summary Aldehydes, ketones and carboxylic acids are some of the important classes of organic compounds containing carbonyl group. These are highly polar molecules. Therefore, they boil at higher temperatures than the hydrocarbons and weakly polar compounds such as ethers of comparable molecular masses. The lower members are more soluble in water because they form hydrogen bonds with water. The higher members, because of large size of hydrophobic chain of carbon atoms, are insoluble in water but soluble in common organic solvents. Aldehydes are prepared by dehydrogenation or controlled oxidation of primary alcohols and controlled or selective reduction of acyl halides. Aromatic aldehydes may also be prepared by oxidation of (i) methylbenzene with chromyl chloride or CrO3 in the presence of acetic anhydride,
(ii) formylation of arenes with carbon monoxide and hydrochloric acid in the presence of anhydrous aluminium chloride, and (iii) cuprous chloride or by hydrolysis of benzal chloride. Ketones are prepared by oxidation of secondary alcohols and hydration of alkynes. Ketones are also prepared by reaction of acyl chloride with dialkylcadmium. A good method for the preparation of aromatic ketones is the Friedel-Crafts acylation of aromatic hydrocarbons with acyl chlorides or anhydrides. Both aldehydes and ketones can be prepared by ozonolysis of alkenes. Aldehydes and ketones undergo nucleophilic addition reactions onto the carbonyl group with a number of nucleophiles such as, HCN, NaHSO3, alcohols (or diols), ammonia derivatives, and Grignard reagents. The α-hydrogens in aldehydes and ketones are acidic.
Therefore, aldehydes and ketones having at least one α-hydrogen, undergo Aldol condensation in the presence of a base to give α-hydroxyaldehydes (aldol) and α-hydroxyketones(ketol), respectively. Aldehydes having no α-hydrogen undergo Cannizzaro reaction in the presence of concentrated alkali. Aldehydes and ketones are reduced to alcohols with NaBH4, LiAlH4, or by catalytic hydrogenation. The carbonyl group of aldehydes and ketones can be reduced to a methylene group by Clemmensen reduction or Wolff-Kishner reduction. Aldehydes are easily oxidised to carboxylic acids by mild oxidising reagents such as Tollens’ reagent and Fehling’s reagent. These oxidation reactions are used to distinguish aldehydes from ketones. Carboxylic acids are prepared by the oxidation of primary alcohols, aldehydes and alkenes by hydrolysis of nitriles, and by treatment of Grignard reagents with carbon dioxide. Aromatic carboxylic acids are also prepared by side-chain oxidation of alkylbenzenes. Carboxylic acids are considerably more acidic than alcohols and most of simple phenols. Carboxylic acids are reduced to primary alcohols with LiAlH4, or better with diborane in ether solution and also undergo α-halogenation with Cl2 and Br2 in the presence of red phosphorus (Hell-Volhard Zelinsky reaction). Methanal, ethanal, propanone, benzaldehyde, formic acid, acetic acid and benzoic acid are highly useful compounds in industry.
What is meant by the following terms ? Give an example of the reaction in each case.
(vii) Ketal (vii) Imine
(x) Schiff’s base 12.2 Name the following compounds according (i)CH3CH(CH3)CH2CH2CHO (ii)CH3CH2COCH(C2H5)CH2CH2Cl
(iii) CH3CH=CHCHO (iv)CH3COCH2COCH3 (v) CH3CH(CH3)CH2C(CH3)2COCH3 (vi)(CH3)3CCH2COOH (vii) OHCC6H4CHO-p 12.3 Draw the structures of the following compounds.
(vi) 3-Bromo-4-phenylpentanoic acid
(viii) Hex-2-en-4-ynoic acid
12.4 Write the IUPAC names of the following ketones and aldehydes.
12.5 Draw structures of the following derivatives.
(i) The 2,4-dinitrophenylhydrazone of benzaldehyde (ii) Cyclopropanone oxime
(iii) Acetaldehydedimethylacetal (iv) The semicarbazone of cyclobutanone (v) The ethylene ketal of hexan-3-one (vi) The methyl hemiacetal of formaldehyde 12.6 Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents. (i) PhMgBr and then H3O+ (ii) Tollens’ reagent (iii) Semicarbazide and weak acid
(iv) Excess ethanol and acid (v) Zinc amalgam and dilute hydrochloric acid 12.7 Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction. (i) Methanal (ii) 2-Methylpentanal
(iii) Benzaldehyde (iv) Benzophenone (v) Cyclohexanone (vi) 1-Phenylpropanone (vii) Phenylacetaldehyde (viii) Butan-1-ol (ix) 2,2-Dimethylbutanal 12.8 How will you convert ethanal into the following compounds? (i) Butane-1,3-diol (ii) But-2-enal
(iii) But-2-enoic acid 12.9 Write structural formulas and names of four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde acts as nucleophile and which as electrophile. 12.10 An organic compound with the molecular formula C9H10O forms 2,4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. Identify the compound. 12.11 An organic compound
(A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved. 12.12 Arrange the following compounds in increasing order of their property as indicated: (i) Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN) (ii) CH3CH2CH(Br)COOH, CH3CH(Br)CH2COOH, (CH3)2CHCOOH, CH3CH2CH2COOH (acid strength) (iii) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength) 12.13 Give simple chemical tests to distinguish between the following pairs of compounds. (i) Propanal and Propanone (ii) Acetophenone and Benzophenone (iii) Phenol and Benzoic acid (iv) Benzoic acid and Ethyl benzoate (v) Pentan-2-one and Pentan-3-one (vi) Benzaldehyde and Acetophenone (vii) Ethanal and Propanal 12.14 How will you prepare the following compounds from benzene? You may use any inorganic reagent and any organic reagent having not more than one carbon atom (i) Methyl benzoate (ii) m-Nitrobenzoic acid (iii) p-Nitrobenzoic acid (iv) Phenylacetic acid (v) p-Nitrobenzaldehyde. 12.15 How will you bring about the following conversions in not more than two steps? (i) Propanone to Propene (ii) Benzoic acid to Benzaldehyde (iii) Ethanol to 3-Hydroxybutanal (iv) Benzene to m-Nitroacetophenone (v) Benzaldehyde to Benzophenone (vi) Bromobenzene to 1-Phenylethanol
(vii) Benzaldehyde to 3-Phenylpropan-1-ol (viii) Benazaldehyde to α-Hydroxyphenylacetic acid (ix) Benzoic acid to m- Nitrobenzyl alcohol 12.16 Describe the following: (i) Acetylation (ii) Cannizzaro reaction (iii) Cross aldol condensation (iv) Decarboxylation 12.17 Complete each synthesis by giving missing starting material, reagent or products
12.18 Give plausible explanation for each of the following:
(i) Cyclohexanone forms cyanohydrin in good yield but 2,2,6-trimethylcyclo- hexanone does not. (ii) There are two –NH2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones. (iii) During the preparation of esters from a carboxylic acid and an alcohol in the presence of an acid catalyst, the water or the ester should be removed as soon as it is formed. 12.19 An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollens’ reagent but forms an addition compound with sodium hydrogensulphite and give positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible structure of the compound.
12.20 Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol.
Answers to Some Intext Questions 12.3 CH3CH2CH3 < CH3OCH3 < CH3CHO < CH3CH2OH 12.4 (i) Butanone < Propanone < Propanal < Ethanal (ii) Acetophenone < p-Tolualdehyde , Benzaldehyde < p-Nitrobenzaldehyde. 12.5
12.6 (i) 3-Phenylpropanoic acid (ii)3-Methylbut-2-enoic acid (iii) 2-Methylcyclopentanecarboxylic acid. (iv) 2,4,6-Trinitrobenzoic acid
12.8 (i) CH3COOH (ii) CH2FCOOH (iii) CH3CHFCH2COOH
Some Useful Links http://www.freelance-teacher.com/videos.htm
I. Multiple Choice Questions (Type-I) 1. Addition of water to alkynes occurs in acidic medium and in the presence of Hg2+ ions as a catalyst. Which of the following products will be formed on addition of water to but-1-yne under these conditions.
3. The correct order of increasing acidic strength is _____________.
(i) Phenol < Ethanol < Chloroacetic acid < Acetic acid (ii) Ethanol < Phenol < Chloroacetic acid < Acetic acid (iii) Ethanol < Phenol < Acetic acid < Chloroacetic acid
(iv) Chloroacetic acid < Acetic acid < Phenol < Ethanol
4. Compound can be prepared by the reaction of _____________. (i) Phenol and benzoic acid in the presence of NaOH (ii) Phenol and benzoyl chloride in the presence of pyridine (iii) Phenol and benzoyl chloride in the presence of ZnCl2 (iv) Phenol and benzaldehyde in the presence of palladium 5. The reagent which does not react with both, acetone and benzaldehyde. (i) Sodium hydrogensulphite (ii) Phenyl hydrazine iii) Fehling’s solution (iv) Grignard reagent 6. Cannizaro’s reaction is not given by _____________.
(iii) HCHO (iv) CH3CHO
Structure of ‘A’ and type of isomerism in the above reaction are respectively.
(i) Prop–1–en–2–ol, metamerism (ii) Prop-1-en-1-ol, tautomerism (iii) Prop-2-en-2-ol, geometrical isomerism (iv) Prop-1-en-2-ol, tautomerism 9. Compounds A and C in the following reaction are __________.
(i) identical (ii) positional isomers (iii) functional isomers (iv) optical isomers 10.
(i) Tollen’s reagent (ii) Benzoyl peroxide (iii) I2 and NaOH solution (iv) Sn and NaOH solution
Which of the following compounds will give butanone on oxidation with alkaline KMnO4 solution? (i) Butan-1-ol (ii) Butan-2-ol (iii) Both of these (iv) None of these 12. In Clemmensen Reduction carbonyl compound is treated with _____________.
(i) Zinc amalgam + HCl (ii) Sodium amalgam + HCl (iii) Zinc amalgam + nitric acid (iv) Sodium amalgam + HNO3 II. Multiple Choice Questions (Type-II)
Note : In the following questions two or more options may be correct. 13. Which of the following compounds do not undergo aldol condensation?
(iii) Sodium benzoate (iv) Benzophenone
15. Which of the following conversions can be carried out by Clemmensen Reduction?
(i) Benzaldehyde into benzyl alcohol
(ii) Cyclohexanone into cyclohexane (iii) Benzoyl chloride into benzaldehyde (iv) Benzophenone into diphenyl methane 16. Through which of the following reactions number of carbon atoms can be increased in the chain?
(i) Grignard reaction (ii) Cannizaro’s reaction (iii) Aldol condensation (iv) HVZ reaction 17. Benzophenone can be obtained by ____________.
(i) Benzoyl chloride + Benzene + AlCl3 (ii) Benzoyl chloride + Diphenyl cadmium (iii) Benzoyl chloride + Phenyl magnesium chloride (iv) Benzene + Carbon monoxide + ZnCl2 18. Which of the following is the correct representation for intermediate of nucleophilic addition reaction to the given carbonyl compound (A) :
III. Short Answer Type 19. Why is there a large difference in the boiling points of butanal and butan-1-ol? 20. Write a test to differentiate between pentan-2-one and pentan-3-one. 21. Give the IUPAC names of the following compounds 22. Give the structure of the following compounds.
24. Benzaldehyde can be obtained from benzal chloride. Write reactions for obtaining benzalchloride and then benzaldehyde from it. 25. Name the electrophile produced in the reaction of benzene with benzoyl chloride in the presence of anhydrous AlCl3. Name the reaction also.
26. Oxidation of ketones involves carbon-carbon bond cleavage. Name the products formed on oxidation of 2, 5-dimethylhexan-3-one. 27. Arrange the following in decreasing order of their acidic strength and give reason for your answer. CH3CH2OH, CH3COOH, ClCH2COOH, FCH2COOH, C6H5CH2COOH 28. What product will be formed on reaction of propanal with 2-methylpropanal in the presence of NaOH? What products will be formed? Write the name of the reaction also. 29. Compound ‘A’ was prepared by oxidation of compound ‘B’ with alkaline KMnO4. Compound ‘A’ on reduction with lithium aluminium hydride gets converted back to compound ‘B’. When compound ‘A’ is heated with compound B in the presence of H2SO4 it produces fruity smell of compound C to which family the compounds ‘A’, ‘B’ and ‘C’ belong to? 30. Arrange the following in decreasing order of their acidic strength. Give explanation for the arrangement. C6H5COOH, FCH2COOH, NO2CH2COOH 31. Alkenes and carbonyl compounds , both contain a π bond but alkenes show electrophilic addition reactions whereas carbonyl compounds show nucleophilic addition reactions. Explain. 32. Carboxylic acids contain carbonyl group but do not show the nucleophilic addition reaction like aldehydes or ketones. Why? 33. Identify the compounds A, B and C in the following reaction.
36. Ethylbenzene is generally prepared by acetylation of benzene followed by reduction and not by direct alkylation. Think of a possible reason.
37. Can Gatterman-Koch reaction be considered similar to Friedel Craft’s acylation? Discuss. 38. Match the common names given in Column I with the IUPAC names given in Column II.
|ColumnI (Common names)||Column II (IUPAC names)|
39. Match the acids given in Column I with their correct IUPAC names given in Column II.
|ColumnI ((Acids))||Column II (IUPAC names)|
|(i)||Phthalic acid||(a)||Hexane-1,6-dioic acid|
|(ii)||Oxalic acid||(b)||Benzene-1,2-dicarboxylic acid|
|(iii)||Succinic acid||(c)||Pentane-1,5-dioic acid|
|(iv)||Adipic acid||(d)||Butane-1,4-dioic acid|
|(v)||Glutaric acid||(e)||Ethane-1,2-dioic acid|
40. Match the reactions given in Column I with the suitable reagents given in Column II.
|ColumnI (Reactions)||Column II (Reagents)|
|(i)||Benzophenone → Diphenylmethane||(a)||LiAlH4|
|(ii)||Benzaldehyde → 1-Phenylethanol||(b)||DIBAL—H|
|(iii)||Cyclohexanone → Cyclohexanol||(c)||Zn(Hg)/Conc. HCl|
|(iv)||Phenyl benzoate → Benzaldehyde||(d)||CH3MgBr|
41. Match the example given in Column I with the name of the reaction in Column II. V. Assertion and Reason Type Note : In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (i) Assertion and reason both are correct and reason is correct explanation of assertion. (ii) Assertion and reason both are wrong statements. (iii) Assertion is correct statement but reason is wrong statement. (iv) Assertion is wrong statement but reason is correct statement.
(v) Assertion and reason both are correct statements but reasson is not correct explanation of assertion. 42. Assertion : Formaldehyde is a planar molecule. Reason : It contains sp2 hybridised carbon atom. 43. Assertion : Compounds containing —CHO group are easily oxidised to corresponding carboxylic acids. Reason : Carboxylic acids can be reduced to alcohols by treatment with LiAlH4.
44. Assertion : The α-hydrogen atom in carbonyl compounds is less acidic. Reason : The anion formed after the loss of α-hydrogen atom is resonance stabilised.
45. Assertion : Aromatic aldehydes and formaldehyde undergo Cannizaro reaction. Reason : Aromatic aldehydes are almost as reactive as formaldehyde.
46. Assertion : Aldehydes and ketones, both react with Tollen’s reagent to form silver mirror. Reason : Both, aldehydes and ketones contain a carbonyl group.
VI. Long Answer Type 47. An alkene ‘A’ (Mol. formula C5H10) on ozonolysis gives a mixture of two compounds ‘B’ and ‘C’. Compound ‘B’ gives positive Fehling’s test and also forms iodoform on treatment with I2 and NaOH. Compound ‘C’ does not give Fehling’s test but forms iodoform. Identify the compounds A, B and C. Write the reaction for ozonolysis and formation of iodoform from B and C. 48. An aromatic compound ‘A’ (Molecular formula C8H8O) gives positive 2, 4-DNP test. It gives a yellow precipitate of compound ‘B’ on treatment with iodine and sodium hydroxide solution.
Compound ‘A’ does not give Tollen’s or Fehling’s test. On drastic oxidation with potassium permanganate it forms a carboxylic acid ‘C’ (Molecular formula C7H6O2), which is also formed along with the yellow compound in the above reaction. Identify A, B and C and write all the reactions involved. 49. Write down functional isomers of a carbonyl compound with molecular formula C3H6O. Which isomer will react faster with HCN and why? Explain the mechanism of the reaction also. Will the reaction lead to the completion with the conversion of whole reactant into product at reaction conditions? If a strong acid is added to the reaction mixture what will be the effect on concentration of the product and why?
50. When liquid ‘A’ is treated with a freshly prepared ammoniacal silver nitrate solution, it gives bright silver mirror. The liquid forms a white crystalline solid on treatment with sodium hydrogensulphite. Liquid ‘B’ also forms a white crystalline solid with sodium hydrogensulphite but it does not give test with ammoniacal silver nitrate. Which of the two liquids is aldehyde? Write the chemical equations of these reactions also.
ANSWERS I. Multiple Choice Questions (Type-I)
1. (ii) 2. (i) 3. (iii) 4. (ii) 5. (iii) 6. (iv) 7. (ii) 8. (iv) 9. (ii) 10. (iii) 11. (ii) 12. (i)
II. Multiple Choice Questions (Type-II) 13. (ii), (iv); [Hint : in compounds (ii) and (iv) α-hydrogen is absent.] 14. (ii), (iii) 15. (ii), (iv) 16. (i), (iii) 17. (i), (ii) 18. (i), (ii)
III. Short Answer Type 19. [Hint : Butan-1-ol has higher boiling point due to intermolecular hydrogen bonding.] 20. [Hint : Iodoform test] 21. (i) 3-Phenylprop-2-enal (ii) Cyclohexanecarbaldehyde (iii) 3-oxopentanal (iv) But -2-enal 22.
29. ‘A’ is a carboxylic acid, ‘B’ is an alcohol and ‘C’ is an ester.
30. NO2CH2COOH > FCH2COOH > C6H5COOH [Hint : electron withdrawing effect.]
31. [Hint : Carbon atom in carbonyl compounds acquires slight positive charge and is attacked by nucleophile.]
IV. Matching Type 38. (i) — (d), (ii) — (e), (iii) — (a), (iv) — (b), (v) — (c) 39. (i) — (b), (ii) — (e), (iii) — (d), (iv) — (a), (v) — (c) 40. (i) — (c), (ii) — (d), (iii) — (a), (iv) — (b) 41. (i) — (e), (ii) — (d), (iii) — (a), (iv) — (b), (v) — (f), (vi) — (c)
V. Assertion and Reason Type 42. (i) 43. (v) 44. (iv) 45. (iii) 46. (iv)
49. CH3CH2CHO CH3COCH3 (I)
(II) • Compound I will react faster with HCN due to less steric hinderance and electronic reasons than
II. • No, It is a reversible reaction. Hence equilibrium is established. • Addition of acid inhibits the reaction because the formation of –CN ions is prevented. 50. Hint : Liquid ‘A’
The following Videos are available for you ( As of Now ). These explain tricky Physics and Mathematics Numericals.
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These covers PU ( Pre University courses, school / college ) courses, IIT JEE, AIEEE ( All India Engineering Entrance Examination ) , CET ( Combined Engineering Test ), AIPMT ( All India Pre Medical Test ), ISc ( Intermediate Science / Indian School Certificate Exam ), CBSE ( Central Board Secondary Exam ), Roorkey Joint Entrance Test Questions ( Discontinued since 2002 ), APhO ( Asian Physics Olympiad ), IPhO ( International Physics Olympiad ), IMO ( International Mathematics Olympiad ) , NSEP ( National Standard Exam in Physics ), RMO ( Regional Math Olympiad , India ), INMO ( Indian National Maths Olympiad ), Irodov Solutions, Prof. H C Verma ( Concepts of Physics ) Solutions etc.
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Zookeeper ;-D Subhashish Chattopadhyay
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Answers to -> Frequently Asked Questions ( FAQ ) [ commonly asked intelligent Questions ]
1 ) How do I prepare for IIT ?
Ans : – See the videos made by me ( in youtube search as Dezrina or “ Zookeeper Physics “ – will see all Uploaded ones. Though we have many more which have not been uploaded ). While watching the videos, take notes and try to solve the problems yourself by pausing the video. Tell me if any calculation is wrong. See the videos with 1- first then 2- and so on. Write to IAPT Kothrud, Pune office to buy ( 150 Rs approx ) the book with previous papers of NSEP ( National Standard Exam in Physics – The 1st level ), INPhO ( Indian National Physics Olympiad – 2nd level ). Prepare with these and see how much you are scoring. You can guess your ALL INDIA rank easily from NSEP, and INPhO rank. Since 1998 the IIT JEE toppers have been mostly representing India in IPhO.
2 ) Some Videos have sound Problem … what do I do ?
Ans : – Only 4 videos have very slight sound echo problem. The same topic got covered again ( many times ) in other videos correctly. The room in which these 4 videos have been recorded had windows only on one side. That gave little bit echo problems. Also external noise of cars, auto, children shouting have randomly come in. You have to have good speakers with filters or good earphones with filters. We have checked mostly it is OK with these. ( If you are depending only on your embedded speakers of computer /screen / keyboard then there may be extra distortions. As these speakers are often not of good Quality. Also install latest KL Codecs ) In any case reduce the volume see the board, imagine sitting in the last bench and solving the problems of your own. See if your solution differs anywhere with the scribbles on the board.
3 ) Why are you giving these ( high Quality ) lecture for free ?
Ans : Well there are lot of good things free in this world. Linux, My-SQL, Open-Office ….. Go to sourceforge and get thousands of high quality software free along with source code. Yes all officially free …. Why do you think Richard Stallman, Zimmerman, ….. etc are considered Guru philosophers ? In Punjab and Gurudwaras worldwide there are so many Langars where you get better food than Restaurants. ….. why ? Why do you have Dharmasalas and subsidized rest rooms near hospitals / Famous Temples / various places ? in Iftar party anyone can eat for free …. why ?
I am teaching for 20 years now and observed most students can do much better if they have the self motivation to solve and practice. Cheap books are available in second hand bookstalls, where you get thousands of Numericals to solve ….. but most students will like to blow their time going and coming for tuition, travel time …. TV for hours and hours watching cricket / Tennis games, playing computer games …. My free lectures are not going to make much difference in spending of unnecessary money for coaching ….. I know very well , how much people enjoy …. ! spending unnecessarily !!
Do you know that there are NO poor / needy students in Bangalore.
Sometime back I had tried to teach for IIT JEE FREE. Discussed with a few NGOs and social service guys. Arranged rooms but got only 1 student. We had informed many people in many ways to inform students …. We did not get students who are ready to learn for free. So I am sure these lectures are NOT FREE. If anyone learns from these, s/he changes and that’s the gain / benefit. This change ( due to learning ) is very costly …. Most do not want to learn ………..
In youtube search for Zookeeper Dezrina you will get most videos. I say most because I do not upload all videos that I make. I have many more videos which are not in the net.
4 ) How can I get all your lectures ?
Ans : – Apart from my lectures there are approx 450GB of PCM ( Phy, Chem, Math ) lectures. It takes approx 3 years of continuous download from scattered sources. I have ( 20,000 )Thousands of these. You can take ALL of them from me in an external 500 GB hard disk, instead of spending so much money and time again for downloading. These cover ( by Various Professors ) everything of Chemistry, Physics, Maths… Lot of this is from outside India … as foreigners have much wider heart than Indians ( as most of GNU / open source software have been developed by Non-Indians ). I observed the gaps in these videos, and thus I am solving IIT, APhO, Roorkey, IPhO Numericals. Videos made by me along with these videos gives a complete preparation.
Send me a mail at firstname.lastname@example.org to contact me.
In youtube search for Zookeeper Dezrina you will get most videos. I say most because I do not upload all videos that I make. I have many more videos which are not in the net.
5 ) How do you get benefited out of this ?
Ans :- If anyone learns we all will have better people in this world. I will have better “ YOU “.
6 ) Why do you call yourself a Zookeeper ?
Ans :- This is very nicely explained at http://zookeepersblog.wordpress.com/z00keeper-why-do-i-call-myself-a-zoookeeper/
7 ) Where do you stay ?
Ans :- Presently I am in Bangalore.
8 ) If I need videos in a few topics can you make them for me ?
Ans :- Yes. You have to discuss the urgency with me. If I am convinced I will surely make these quickly for you and give you and ALL. I teach both Maths and Physics. So anything in these 2 subjects are welcome.
9 ) Why did you write an article saying there are No Poor students ?
Ans :- There are lots of NGOs and others working for rural / poor children education at lower classes. While very less effort is on for std 9 till 12. Also see the answer in question number ( 3 ) above. In last 20 years of teaching I never met a Poor child who was seriously interested in ( higher ) studies. As I have a mind / thinking of a ” Physicist “, I go by ” Experimental Observation “.
It is not about what is being said about poor in media / TV etc, or ” what it should be ” ( ? ) …. It is about what I see happening. Also to add ( confuse ? you more )…. You must be knowing that in several states over many years now girl students have better ( by marks as well as by pass percentage ) result in std 10 / Board Exams….. well but NEVER a girl student came FIRST in IIT JEE … why ? [ The best rank by a Girl student is mostly in 2 digits, very rarely in single digit ] ????? So ????
10 ) How much do I have to study to make it to IIT ?
Ans :- My experience of Teaching for IIT JEE since last 20 years, tells me, Total 200 hours per subject ( PCM ) is sufficient. If you see my Maths and Physics videos, each subject is more than 200 hours. So if someone sees all the videos deligently, takes notes and remembers, …… Done.
11 ) What is EAMCET ?
Ans :- Engineering Agriculture and Medicine Common Entrance Test is conducted by JNT University Hyderabad on behalf of APSCHE. This examination is the gateway for entry into various professional courses offered in Government/Private Colleges in Andhra Pradesh.
12 ) In your videos are you covering other Exams apart from IIT ?
Ans : – Yes. See many videos made by solving problems of MPPET, Rajasthan / J&K CET, UPSEAT ( UPES Engineering Aptitude Test ), MHCET, BCECE ( Bihar Combined Entrance Competitive Examination Board ), WB JEE etc
13 ) What is SCRA ?
Ans : – Special Class Railway Apprentice (SCRA) exam is conducted by Union Public Service Commission (UPSC) board, for about 10 seats.That translates into an astonishing ratio of 1 selection per 10,000 applicants. The SCRA scheme was started in 1927 by the British, to select a handful of most intelligent Indians to assist them in their Railway Operations, after training at their Railway’s largest workshop, i.e. Jamalpur Workshop, and for one year in United Kingdom. The selected candidates were required to appear in the Mechanical Engineering Degree Exmination held by Engineering Council (London).
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Temperature-Sea Levels-CO2-etc always have been fluctuating over ages-Global Warming
The following video is a must see for full CO2 cycle, plates of Earth, Geological activities, stability of weather
The Great Global Warming swindle
Article in Nature says CO2 increase is good for the trees
BBC documentary Crescent and Cross shows the 1000 years of fight between Christians and Muslims. Millions have been killed in the name of Religion. To decided whose GOD is better, and which GOD to follow. The fight continues.
The Virus of Faith
The God delusion
cassiopeia facts about evolution http://www.youtube.com/watch?v=K7tQIB4UdiY
Intermediate Fossil records shown and explained nicely Fossils, Genes, and Embryos http://www.youtube.com/watch?v=fdpMrE7BdHQ
The Rise Of Narcissism In Women http://www.youtube.com/watch?v=wZHKCbHGlS0
13 type of women whom you should never court
Media teaching Misandry in India http://www.youtube.com/watch?v=-M2txSbOPIo
Summary of problems with women http://problemwithwomentoday.blogspot.in/2009/12/problem-with-women-today-what-in-hell.html
Eyeopener men ? women only exists http://www.youtube.com/watch?v=6ZAuqkqxk9A
Most unfortunate for men http://www.youtube.com/watch?v=73fGqUwmOPg
Miracles for Sale http://www.youtube.com/watch?v=iuP5uOI7Xwc
The Enemies of Reason http://www.youtube.com/watch?v=0CyMglakWoo
Each of you is an Activist in some way or other. You are trying to propagate those thoughts, ideas that you feel concerned / excited about.
Did you analyze your effectiveness ?
http://www.youtube.com/watch?v=61qn7S9NCOs Culturomics can help you
Why some temples become ” FAMOUS ” ? How you can be manipulated ? Luck for others ?
see how biased women are. Experimental proof. Women are happy when they see another woman is beating a man ( see how women misbehave with men )
see detailed statistics at http://www.youtube.com/watch?v=5lHmCN3MBMI
An eye opener in Misandry http://www.youtube.com/watch?v=YiTaDS_X6CU
My sincere advice would be to be EXTREMELY careful ( and preferably away ) of girls. As girls age; statistically certain behavior in them has been observed. Most Male can NOT manage those behaviors… Domestic violence, divorce etc are rising very fast. Almost in all cases boys / males are HUGE loosers. Be extremely choosy ( and think from several angles ) before even talking to a girl.
How women manipulate men http://www.angryharry.com/esWomenManipulateMen.htm
Gender Biased Laws in India http://zookeepersblog.wordpress.com/biased-laws/
Violence against Men http://www.youtube.com/watch?v=MLS2E-rRynE
Only men are victimised http://www.youtube.com/watch?v=4JA4EPRbWhQ
Men are BETTER than women http://www.menarebetterthanwomen.com/
Male Psychology http://www.youtube.com/watch?v=uwxgavf2xWE
Women are more violent than men http://www.independent.co.uk/news/uk/home-news/women-are-more-violent-says-study-622388.html
Misandry in Media http://www.youtube.com/watch?v=j7U0r7vIrgM
In the year 2010, 168 men ended their lives everyday ( on average ). More husbands committed suicide than wives.
It is EXTREMELY unfortunate that media projects men as fools, women as superiors, Husbands as servants, and replaceable morons. In ad after ad worldwide from so many companies, similar msg to disintegrate the world is being bombarded. It is highly unacceptable misandry
It is NOT at all funny that media shows violence against MEN. Some advertisers are trying to create a new ” Socially acceptable culture ” of slapping Men ( by modern city women ). We ( all men ) take objection to these advertisements.
We oppose this Misandry bad culture. Please share to increase awareness against Men bashing
Are you a nice person ? Just shout Wooooooooo , Eyye Eyye and enjoy to see someone in trouble ….
Extension of Milgram Experiments – In a Mob also people become cruel step by step -
Think what are you doing … why are you doing ? http://www.youtube.com/watch?v=qp0HIF3SfI4
Every Man must know this … http://www.youtube.com/watch?v=cIFmQHJEG1M
Manginas, White Knights, & Other Chivalrous Dogs http://www.youtube.com/watch?v=oXQDtBT70B8
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